Atmospheric Environment 36 (2002) 1147–1161 Application of a model system for the study of transport and diffusion in complex terrain to the TRACT experiment J.C. Carvalho a, *, D. Anfossi b , S. Trini Castelli b,c , G.A. Degrazia d a Faculdade de Engenharia Ambiental, Universidade Luterana do Brasil, Curso de Engenharia Ambiental, Programa de P ! os-Gradua , c * ao em Engenharia: Energia, Ambiente e Materiais, 92420-280 Canoas, RS, Brazil b C.N.R., Istituto di Cosmogeofisica, 10133, Torino, Italy c Universit " a, Dipartimento di Scienze e Tecnologie Avanzate, 15100, Alessandria, Italy d Universidade Federal de Santa Maria, Departamento de F! ısica, 97105-900 Santa Maria, RS, Brazil Received 2 April 2001; received in revised form 25 October 2001; accepted 16 November 2001 Abstract The transport and diffusion processes of a tracer gas released near the ground in the Rhine valley region, in Central Europe, during the 1992 TRACT field experiment, are simulated by a computational model system for complex terrain. Thissystem(RMS)iscomposedoftheprognosticmesoscalemodelRAMS,theLagrangianstochasticdispersionmodel SPRAY and the interface code MIRS, which links RAMS to SPRAY. Three flow simulations were performed, with different initialisations and the one showing the best agreement with the measured flow was selected for the simulation of the TRACT tracer experiment. Tracer concentrations measured by an array of samplers at ground level and by an airplane aloft, are used to evaluate the 3-D concentration field simulated by the model system. The analysis of the simulation results generated by RMS shows that our model system very well reproduces the general behaviour of the contaminant plume, the temporal and spatial distribution of the concentration and the location of the concentration maxima. r 2002 Elsevier Science Ltd. All rights reserved. Keywords: Atmospheric dispersion; Lagrangian model; Tracer experiment; Model initialisation; Turbulence parameterisation 1. Introduction Correctly predicting the pollutant dispersion in complex inhomogeneous terrain is of great importance and, at the same time, it is a difficult task. The presence of complex terrain causes spatial (both in the horizontal and in the vertical direction) and temporal variations of the flow and turbulence conditions that strongly influence the pollutant dispersion. In the presence of these perturbed circulations, ground level concentration (g.l.c.) values are determined by inhomogeneous and non-stationary air trajectories, which drive the pollutant transport. In view of this, simplest types of dispersion models, based on the Gaussian-type formulations or on K-theory, cannot be used with sufficient reliability in complex terrain, as was shown, for instance, by Brown et al. (1993). Consequently, the application of a model system, composed of a meteorological model coupled to a dispersion model may be recommended. In these model systems, the meteorological model provides the inhomogeneous and non-stationary three-dimensional (3-D) meteorological fields and the dispersion model calculates the 3-D concentration fields, allowing a more adequate description of the atmospheric pollutant dispersion. The investigations carried out, for instance, by Yamada et al. (1992), Physicks et al. (1994), Boybeyi et al. (1995), Anfossi et al. (1998) and Tinarelli et al. (2000) are good examples of the potentialities of these kinds of simulation systems. In the present work, a computational modelling system (RMS), composed of the meteorological model *Corresponding author. Tel.: +55-51-477-9285; fax: +55- 51-477-1313. E-mail address: jonas@ccne.ufsm.br, jonas@ulbra.tche.br (J.C. Carvalho). 1352-2310/02/$-see front matter r 2002 Elsevier Science Ltd. All rights reserved. PII:S1352-2310(01)00559-3